1. Field of the Invention
This invention relates to a method and apparatus for determining an etching rate. More particularly, it relates to a method and apparatus for determining the etching rate at which light metals and alloys thereof, such as aluminum, aluminum alloys, magnesium and magnesium alloys, are etched with acid or alkali etchants.
2. Description of the Related Art
In the etching art, aluminum parts are often subject to a pretreatment by immersing them in acid or alkali liquid etchants for etching the surface thereof prior to customary surface treatments, like anodizing and plating. For such a pretreatment, it is desired in view of management of the etchant to monitor the etching ability of the etchant by measuring the etching rate.
Several techniques are known for the measurement of etching rate, including a weighing technique for measuring the quantity (in mg unit) of metal etched away per unit time, and a coulostatic technique of applying a potential to an electrode immersed in the etchant, and measuring the time taken until the potential becomes constant.
However, the weighing technique presents a problem in that, because measurement cannot be carried out in a reaction system for actual treatment, another system containing a measurement specimen must be used for measurement, from which the etching rate associated with actual etching can only be presumed. This can lead to a time lag, and requires a large sized measuring system. The coulostatic technique also requires a large apparatus, and increases the cost of etching rate measurement.